The event "Joe Hisaishi - Music from the Studio Ghibli Films of Hayao Miyazaki"
is no longer available in Stubhub list and I have not yet received any tickets. How can I claim a refund for two tickets I purchased?
Radio City web site shows this event as postponed. When an event is in a POSTPONED status then you can't request a refund because the original tickets are valid for the rescheduled event. If the event is canceled and not rescheduled then you should reach out to Stubhub to find out your options.